The conductive paste is a material in which metal particles are dispersed in a vehicle comprising an organic binder and a solvent, and it has been used for formation of a conductor pattern of a printed wiring board or formation of an external electrode of a laminated ceramic electronic part, etc. In the conductive paste, there are a resin curing type in which conductivity is ensured by contacting the metal particles due to curing of the resin, and a sintering type in which conductivity is ensured by sintering of the metal particles to each other by sintering.
As the metal particles to be contained in the conductive paste, for example, copper powder or silver powder has been used. The copper powder has the merits that it is excellent in conductivity and inexpensive than that of the silver powder. However, the copper powder is likely oxidized in the atmosphere so that there is a defect that, for example, the surface of a conductor pattern must be covered by a protecting material after forming the conductor pattern onto a substrate. On the other hand, the silver powder has merits that it is stable in the atmosphere, and a conductor pattern can be formed by sintering in the atmosphere. However, the silver powder has a defect that it easily causes electromigration.
As a technique to prevent from electromigration, in Patent Document 1, there is disclosed a conductive paint which comprises silver powder as a main conductive material and contains 1 to 100 parts by mass of powder of manganese and/or manganese alloy based on 100 parts by mass of the silver powder. In Patent Document 2, there is disclosed a conductive paste containing a binder resin, Ag powder and at least one metal or metallic compound selected from the group consisting of Ti, Ni, In, Sn and Sb.
However, the conductive pastes disclosed in Patent Documents 1 and 2 are insufficient in adhesiveness to the substrate or solder heat resistance, so that there is a practical problem for using these for formation of a conductor pattern onto the substrate.
Thus, as a technique to improve solder heat resistance of the conductive paste, in Patent Document 3, there is disclosed a conductive paste in which silver powder is coated by a material containing a first metal component which suppress sintering of the silver and a second metal component which promotes sintering of the silver.
However, in the conductive paste disclosed in Patent Document 3, solder heat resistance can be improved with a certain extent, but there is a problem that sintering of the silver is suppressed so that conductivity of the conductor pattern obtained by sintering the conductive paste is lowered. In addition, a step of coating a metal material onto the surface of the silver powder is required so that there is a problem that the manufacturing process becomes complex.